The system specifically described in the above-identified patent comprises, as a first and a second drive-establishing means, a unidirectionally effective and a bidirectionally effective brake which are both filled with high-pressure hydraulic fluid upon an upshift from a low-speed position ("first gear") into an intermediate-speed position ("second gear"), the engagement of both brakes being moderated by a control valve which in its normal position admits fluid to them at a relatively high rate but which, upon incipient pressure buildup in the unidirectionally effective first brake, is moved by fluid feedback into an off-normal position resulting in a throttled flow. After the fluid pressure in the first brake (which at this stage is directly connected to the second brake) has reached a predetermined level, the normal position of the control valve is re-established by a force-increasing action of that fluid pressure upon a biasing member opposing the off-normal displacement of this valve. Thus, the two brakes are under full supply pressure as soon as the upshift into second gear is completed.
A further upshift into a high-speed position ("third gear") requires the release of the bidirectionally effective second brake. This release is brought about by the draining of the feeder line of that brake via the normally positioned control valve and a 2-3 shift valve in tandem therewith. In the event of a subsequent downshift to second gear, the first brake is already actuated so that only the second brake need be supplied with fluid; this occurs in response to a return of the 2-3 shift valve from an upshifting to a downshifting position, with no further intervention of the control valve in tandem therewith.
If the upshift into third gear occurs before the second-gear position is fully established, i.e. with the control valve still in its off-normal throttling position, the draining of the bidirectionally effective brake cannot take place immediately but must await the restoration of the control valve to normal. The resulting delay may lead to concurrent actuation of the two brakes and of a clutch effective in third gear only whereby, with these three drive-establishing means acting upon a common movable element (shaft) of a planetary-gear transmission, the system jams for brief periods during which the affected components are subjected to excessive stress.